The present invention relates to blends of one or more metal cation neutralized acid copolymers with one or more metal cation neutralized ethylene acrylates, and to improved golf ball covers made from these blends. More particularly, the invention relates to golf ball covers produced from blends of at least one metal cation neutralized olefin-carboxylic acid copolymer, such as ethylene acrylic or methacrylic acid copolymer, and at least one metal cation (preferably alkali metal cation) hydrolyzed and neutralized ethylene alkyl acrylate copolymer. The improved golf ball covers are useful for producing golf balls exhibiting the desired travel distance while maintaining or improving the playability and/or durability characteristics necessary for repetitive play.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E.I. DuPont de Nemours and Company under the trademark xe2x80x9cSurlyn(copyright)xe2x80x9d and more recently, by the Exxon Corporation under the trademarks xe2x80x9cEscor(copyright)xe2x80x9d and the tradename xe2x80x9cIotek(trademark)xe2x80x9d, have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability properties required for repetitive play.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. In some instances, an additional softening comonomer can also be included to form a terpolymer. The pendent ionic groups in the ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. The metal ions, such as sodium, zinc, magnesium, lithium, potassium, calcium, etc. are used to neutralize some portion of the acid groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc. for golf ball construction over balata.
Broadly, the ionic copolymers comprise one or more alpha-olefins and from about 9 to about 30 weight percent of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid, the basic copolymer neutralized with metal ions to the extent desired. Usually, at least 20% of the carboxylic acid groups of the copolymer are neutralized by the metal ions (such as sodium, potassium, manganese, zinc, lithium, calcium, nickel, magnesium, and the like) and exist in the ionic state. In general, ionic copolymers including up to 16% acid are considered xe2x80x9clow acidxe2x80x9d ionomers, while those including greater than 16% acid are considered xe2x80x9chigh acidxe2x80x9d ionomers by the present inventors.
Suitable olefins for use in preparing the ionomeric resins include ethylene, propylene, butene-1, hexene-1, and the like. Unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, xcex1-chloroacrylic, crotonic, maleic, fumaric, itaconic acids, and the like. The ionomeric resins utilized in the golf ball industry are generally copolymers of ethylene with acrylic (i.e. Escor(copyright) or Iotek(trademark)) and/or methacrylic (i.e. Surlyn(copyright)) acid. In addition, two or more types of ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.
Along this line, the properties of the cover compositions and/or the ionomeric resins utilized in the golf ball industry vary according to the type and amount of the metal cation, the molecular weight, the composition of the base resin (i.e. the nature and the relative content of the olefin, the unsaturated carboxylic acid groups, etc.), the amount of acid, the degree of neutralization and whether additional ingredients such as reinforcement agents or additives are utilized. Consequently, the properties of the ionomer resins can be controlled and varied in order to produce golf balls having different playing characteristics, such as differences in hardness, playability (i.e. spin, feel, click, etc.), durability (i.e. impact and/or cut resistance), and resilience (i.e. coefficient of restitution).
However, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups), the degree of neutralization and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the playability characteristics previously associated with the balata cover, but also the improved impact resistance and carrying distance properties produced by the ionomeric resins. Thus, an object of the present invention is to provide golf ball cover compositions which, when utilized in golf ball construction, produce balls exhibiting the desired travel distance (i.e., similar coefficient of restitution values) while maintaining or improvity satisfactory playability and durability properties.
A golf ball""s coefficient of restitution, (C.O.R.) is the ratio of the relative velocity of the ball after direct impact to that before impact. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming velocity and outgoing velocity. The coefficient of restitution is defined as the ratio of the outgoing velocity to incoming velocity of a rebounding ball and is expressed as a decimal. As a result, the coefficient of restitution can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.
The coefficient of restitution of a one-piece golf ball is a function of the ball""s composition. In a two-piece or a multi-layered golf ball, the coefficient of restitution is a function of the core, the cover and any additional layer. While there are no United States Golf Association (U.S.G.A.) limitations on the coefficient of restitution values of a golf ball, the U.S.G.A. requires that the golf ball cannot exceed an initial velocity of 255 feet/second. As a result, golf ball manufacturers generally seek to maximize the coefficient of restitution of a ball without violating the velocity limitation.
In various attempts to produce a high coefficient of restitution golf ball exhibiting the enhanced travel distance desired, the golfing industry has blended various ionomeric resins. However, many of these blends do not exhibit the durability and playability characteristics necessary for repetitive play and/or the enhanced travel distance desired.
It is, therefore, desirable to develop cover compositions which produce golf balls exhibiting properties of desired carrying distance (i.e., possess desirable coefficient of restitution values) such as the ionomeric cover blends set forth in U.S. Pat. Nos. 4,884,814 and 4,911,451, without sacrificing or improving playability and/or durability characteristics.
Furthermore, while as stated above, Surlyn(copyright) and Escor(copyright) (or xe2x80x9cIotek(trademark)xe2x80x9d) are materials of choice for golf ball cover construction when balata (natural or synthetic) is not used, these materials are relatively costly and available from limited sources. It has, therefore, become desirable to develop alternative ionomer resin based compositions having properties suitable for use to in golf ball cover construction.
These and other objects and features of the invention will be apparent from the following description and from the claims.
The present invention is directed to golf ball covers, and more specifically to golf ball cover compositions which comprise blends of one or more metal cation neutralized olefin-carboxylic acid copolymers, such as ethylene acrylic or methacrylic acid copolymers, and one or more metal cation (preferably alkali metal cation) neutralized ethylene alkyl acrylate copolymers. The golf ball covers of the invention provide desirable alternatives to covers produced from the Surlyn(copyright) and Iotek(trademark) ionomeric resins currently used in golf ball cover construction.
The present invention is particularly directed to golf ball cover compositions which are prepared by blending at least one metal cation neutralized acid copolymer which contains about 1% to about 30% carboxylic acid, with at least one alkali metal cation hydrolyzed and neutralized ethylene alkyl acrylate copolymers containing up to about 30% by weight of an alkyl acrylate. The alkyl acrylate in the ethylene copolymer is any acrylic or methacrylic esters of linear, branched or cyclic alkanols having 1-28 carbon atoms including, among others, ethyl acrylate, methyl acrylate and butyl acrylate. The ethylene copolymers may, therefore, comprise ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EMA), and/or ethylene butyl acrylate (EBA) among others.
The selection of type and ratio of the metal cation neutralized acid copolymer, such as ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer, etc., to the alkali metal cation neutralized ethylene alkyl acrylate copolymer (i.e., EEA, EMA, EBA, etc.) is based on the desired final hardness, durability, travel distance and spin rate of the ball. Preferably, the blend of the metal cation neutralized acid copolymer and the alkali metal cation neutralized ethylene alkyl acrylate includes about 0 to 90 parts by weight acid copolymer, and about 100 to 10 parts by weight ethylene alkyl acrylate. More preferably, the blend is comprised of about 0 to 75 parts by weight partially neutralized acid copolymer and about 100 to 25 parts by weight hydrolyzed and neutralized ethylene alkyl acrylate. Most preferably the blend consists of about 0 to about 50 parts by weight neutralized acid copolymer and about 100 to 50 parts by weight neutralized and hydrolyzed ethylene alkyl acrylate.
In another aspect, the invention relates to a cover composition comprising a blend of i) a metal cation neutralized copolymer of about 1 weight percent to about 30 weight percent, preferably 9 to 25 weight percent of an alpha, beta-unsaturated carboxylic acid (preferably acrylic acid or methacrylic acid) and an olefin (preferably ethylene), and ii) an metal cation (preferably alkali metal cation) neutralized ethylene alkyl acrylate (preferably ethylene methyl acrylate and ethylene butyl acrylate). Approximately, 10% to about 90% of the carboxyl groups of the acid copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, calcium, manganese, zinc, sodium, and nickel. In addition, the carboxylic acid esters of the ethylene alkyl acrylate copolymers are hydrolysized or neutralized though the use of alkali metal cations.
In another further aspect, the invention relates to a golf ball comprising a core and a cover, wherein the cover is comprised of a blend of i) a metal cation neutralized copolymer of about 1 to 30% by weight of an acrylic acid and the remainder ethylene and ii) an alkali metal cation neutralized ethylene alkyl acrylate. Approximately, 10% to 90% of the carboxyl groups of the acrylic acid/ethylene copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, sodium, zinc, magnesium, calcium and nickel. Moreover, the carboxylic acid esters of the ethylene alkyl acrylate copolymer are hydrolysized and neutralized by an alkali metal cations such as lithium, sodium and potassium. In addition, the cover may contain one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners. The core is generally a solid core.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
The present invention relates to the development of golf balls, and more particularly to golf ball cover compositions which comprise blends of one or more acid copolymers with one or more hydrolyzed and neutralized neutralized ethylene copolymers (i.e., ethylene alkyl acrylates). Golf ball covers having good durability, playability (spin) and C.O.R. characteristics are provided.
The acid copolymer used herein may contain anywhere from 1 to 30 percent by weight acid. In some instances, it is preferable to utilize a high acid copolymer (i.e. a copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably about 20 weight percent acid). The acid copolymer is neutralized with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired (i.e. generally from about 10% to 90%).
The base acid copolymer is preferably made up of from about 10 to about 30% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, a softening comonomer can be included in the copolymer. Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons. Examples of such acids include acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.
The softening comonomer that can be optionally included in the invention may be selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms and vinyl ethers wherein the alkyl groups contain 1 to 10 carbon atoms.
Consequently, examples of a number of copolymers suitable for use in the invention include, but are not limited to, an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, an ethylene/methacrylic acid/vinyl acetate copolymer, an ethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymer broadly contains 1 to about 30% by weight unsaturated carboxylic acid, from about 70 to about 99% by weight ethylene and from 0 to about 40% by weight of a softening comonomer.
Along these lines, examples of low acid based copolymers which fulfill the criteria set forth above include but are not limited to the Esco(copyright) 5000, 5001, 5020, 5050, 5070, 5100, 5110 and 5200 low acid ethylene-acrylic acid copolymers sold by Exxon and the Primacor(trademark) 1321, 1410, 1410-XT, 1420, 1430, 2912, 3150, 3330, 3340, 3440, 3460, 4311 and 4608 ethylene-acrylic acid copolymers sold by Dow Chemical Company, Midland, Mich. Typical properties of these low acid based copolymers are indicated below in Tables 1A-1C.
Further, examples of high acid base copolymers which fulfill the criteria set forth above, are a series of ethylene-acrylic acid copolymers which are commercially available from The Dow Chemical Company, Midland, Mich., under the xe2x80x9cPrimacorxe2x80x9d designation. These high acid base copolymers exhibit the typical properties set forth below in Table 2.
Other acid copolymers which may be used include an ethylene-methacrylic acid copolymer such as Nucrel(copyright) available from E.I. DuPont de Nemours and Co. Nucrel(copyright) is an ethylene copolymer which is inherently flexible like EVA copolymers, and which offers desirable performance characteristics similar to those of Surlyn(copyright) ionomers.
The Nucrel(copyright) acid copolymers are produced by reacting ethylene and methacrylic acid in the presence of free radical initiators. A branched, random ethylene methacrylic acid (EMAA) copolymer is produced thereby. Carboxyl groups are distributed along the chain and interact with carboxyl groups on adjacent molecules to form a weakly cross-linked network through hydrogen bonding.
Nucrel(copyright) ethylene copolymers offer tensile strength as high as 25 MPa (3,600 psi) and good performance at low temperatures (945 k J/m2 at xe2x88x9240xc2x0 C.). Properties of selected Nucrel(copyright) ethylene copolymers are listed in Table 3.
The acid copolymers used in the invention are neutralized to a certain percentage through the use of metal cation salts. The metal cation salts utilized are those salts which provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the acid copolymer. These include acetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel, magnesium, and manganese.
Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Sources for the calcium ion include calcium hydroxide, calcium acetate and calcium oxide. Suitable zinc ion sources are zinc acetate dihydrate and zinc acetate, a blend of zinc oxide and acetic acid. Examples of sodium ion sources are sodium hydroxide and sodium acetate. Sources for the potassium ion include potassium hydroxide and potassium acetate. Suitable nickel ion sources are nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium include magnesium oxide, magnesium hydroxide, magnesium acetate. Sources of manganese include manganese acetate and manganese oxide.
Additionally a wide variety of pre-neutralized acid copolymers are commercially available. These include both hard and soft pre-neutralized ionomer resins and both low and high acid pre-neutralized ionomer resins.
The hard (high modulus) pre-neutralized ionomers include those ionomers having a hardness greater than 50 on the Shore D scale as measured in accordance with ASTM method D-2240, and a flexural modulus from about 15,000 to about 70,000 psi as measured in accordance with ASTM method D-790.
Although the scope of the patent embraces all known hard ionomeric resins falling within the parameters set forth above, only a relatively limited number of these hard ionomeric resins are commercially available. In this regard, the hard ionomeric resins sold by E.I. DuPont de Nemours Company under the trademark xe2x80x9cSurlyn(copyright)xe2x80x9d, and the hard ionomer resins sold by Exxon Corporation under either the trademark xe2x80x9cEscor(copyright) xe2x80x9d or the tradename xe2x80x9cIotek(trademark)xe2x80x9d are examples of commercially available hard ionomeric resins which may be utilized in the present invention.
The hard ionomeric resins introduced under the designation xe2x80x9cEscor(copyright)xe2x80x9d and now sold under the new designation xe2x80x9cIotek(trademark)xe2x80x9d, are somewhat similar to the hard ionomeric resins sold under the xe2x80x9cSurlyn(copyright)xe2x80x9d trademark. However, since the xe2x80x9cIotek(trademark)xe2x80x9d ionomeric resins are sodium or zinc salts of poly(ethylene acrylic acid) and the xe2x80x9cSurlyn(copyright)xe2x80x9d resins are zinc or sodium salts of poly(ethylene methacrylic acid) some distinct differences in properties exist. In addition, various blends of xe2x80x9cIotek(trademark)xe2x80x9d and xe2x80x9cSurlyn(copyright)xe2x80x9d hard ionomeric resins, as well as other available ionomeric resins, may be utilized in the present invention.
Examples of commercially available hard ionomeric resins which may be utilized in the present invention include the hard sodium ionic copolymer sold under the trademark xe2x80x9cSurlyn(copyright) 8940xe2x80x9d and the hard zinc ionic copolymer sold under the trademark xe2x80x9cSurlyn(copyright) 9910xe2x80x9d. Surlyn(copyright) 8940 is a copolymer of ethylene with methacrylic acid with about 15 weight percent acid which is about 29% neutralized with sodium ions. This resin has an average melt flow index of about 2.8. Surlyn(copyright) 9910 is a copolymer of ethylene and methacrylic acid with about 15 weight percent acid which is about 58% neutralized with zinc ions. The average melt flow index of Surlyn(copyright) 9910 is about 0.7. The typical properties of Surlyn(copyright) 9910 and 8940 are set forth below in Table 4.
In addition, examples of acrylic acid based hard ionomer resins suitable for use in the present invention include those sold under the xe2x80x9cIotek(trademark)xe2x80x9d tradename by the Exxon Corporation. Examples of such acrylic acid based hard ionomer resins are xe2x80x9cIotek(trademark) 4000xe2x80x9d (formerly xe2x80x9cEscor 4000xe2x80x9d), xe2x80x9cIotek(trademark) 4010xe2x80x9d, xe2x80x9cIotek(trademark) 8000xe2x80x9d (formerly Escor 900), xe2x80x9cIotek(trademark) 8020xe2x80x9d, and xe2x80x9cIotek(trademark) 8030xe2x80x9d. The typical properties of the Iotek(trademark) hard ionomers are set forth below in Table 5.
Further, as indicated above, pre-neutralized soft ionomer resins can also be used in the present invention. The soft (low modulus) pre-neutralized ionomers are generally acrylic acid or methacrylic acid based soft ionomers. Preferably, the soft pre-neutralized ionomer is a zinc based ionomer made from an acrylic acid base polymer and an unsaturated monomer of the acrylate ester class. The soft (low modulus) ionomers have a hardness from about 20 to about 40 (preferably from about 30 to about 40) as measured on the Shore D scale and a flexural modulus from about 2,000 to about 10,000 psi (preferably from about 3,000 to 7,000 psi) as measured in accordance with ASTM method D-790.
Examples of such soft pre-neutralized ionomer resins include Surlyn(copyright) 8265 and 8269. These are sodium neutralized methacrylic acid based ionomers having a Shore D hardness of 25-40 and a flex modulus of 2,000-10,000.
More preferably, the inventors have found that when the new ethylene-acrylic acid based soft pre-neutralized ionomer resins recently developed by the Exxon Corporation under the designations xe2x80x9cIotek(trademark) 7520xe2x80x9d(referred experimentally by differences in neutralization and melt indexes as LDX 195, LDX 196, LDX 218 and LDX 219) are used either alone or combined with hard pre-neutralized ionomers, the compositions produce higher C.O.R.s at equal or softer hardness, higher melt flow (which corresponds to improved, more efficient molding, i.e. fewer rejects), as well as significant cost savings versus balls produced by the pre-neutralized methacrylic acid ionomer blends due to lower overall raw materials cost and improved yields.
While the exact chemical composition of the resins to be sold by Exxon under the designation Iotek(trademark) 7520 is considered by Exxon to be confidential and proprietary information, Exxon""s Experimental Product Data sheet lists the following physical properties of this ethylene acrylic acid zinc ionomer developed by Exxon:
In addition, test data collected by the inventors indicate that Iotek(trademark) 7520 resins have Shore D hardnesses of about 32-36 (per ASTM D-2240), melt flow indexes of 3xc2x15 g/10 min (at 190xc2x0 C. per ASTM D-1288), a flexural moduluses of about 2500-3500 psi (17-24 MPa)(per ASTM D-790). Furthermore, testing by an independent testing laboratory by pyrolysis mass spectrometry indicates that the Iotek(trademark) 7520 resins are generally zinc salts of a terpolymer of ethylene, accrylic acid, and methyl acrylate.
Moreover, the inventors have found that a newly developed grade of an acrylic acid based soft pre-neutralized ionomer available from Exxon Corporation under the designation Iotek(trademark) 7510, is also effective in producing golf ball covers exhibiting higher C.O.R. values at equal or softer hardness than those produced by the methacrylic acid ionomer blends. In this regard, Iotek(trademark) 7510 has the advantages (i.e. improved flow, higher C.O.R. values at equal hardness, increased clarity, etc.) produced by the Ioteck(trademark) 7520 resin when compared to the methacrylic acid base soft ionomers known in the art (such as the Surlyn(copyright) 8625 and the Surlyn(copyright) 8629).
In addition, Iotek(trademark) 7510, when compared to Iotek(trademark) 7520, produces slightly higer C.O.R. values at equal softness/hardness due to the Iotek(trademark) 7510""s higher hardness and neutralization. Similarly, Iotek(trademark) 7510 produces better releas properties (from the mold cavities) due to its slightly higer stiffness and lower flow rate than Iotek(trademark) 7520. Consequently, Iotek(trademark) 7510 is the more preferred soft ionomer used in the invention.
According to Exxon, Iotek(trademark) 7510 is of similar chemical composition as Iotek(trademark) 7520 (i.e. a zinc salt of a terpoloymer of ethylene, acrylic acid, and methyl acrylate) but is more highly neutralized. Based upon FTIR analisis, Iotek(trademark) 7520 is estimated to be about 30-40 wt.-% neutralized and Iotek(trademark) 7510 is estimated to be about 40-60 wt.-% neutralized. The typical properties of Iotek(trademark) 7510 in comparasion of those of Iotek(trademark) 7520 are set forth below.
Moreover, in addition to the pre-neutralized low acid ionomer resins, several pre-neutralized high acid ionomer resins are now commercially available. Examples of the high acid methacrylic acid based ionomers suitable for use in accordance with this invention include Surlyn(copyright) AD-8422 (sodium cation), Surlyn(copyright) 8162 (zinc cation), Surlyn(copyright) SEP-503-1 (zinc cation), and Surlyn(copyright) SEP-503-2 (magnesium cation). According to Dupont, all of these ionomers contain from about 18.5 to about 21.5% by weight methacrylic acid.
More particularly, Surlyn(copyright) AD-8422, is currently commercially available from DuPont in a number of different grades (i.e. AD-8422-2, AD-8422-3, AD-8422-5, etc.) based upon differences in melt index. According to DuPont, Surlyn(copyright) AD-8422 offers the following general properties when compared to Surlyn(copyright) 8920 the stiffest, hardest of all of the low acid grades:
In comparing Surlyn(copyright) 8920 to Surlyn(copyright) 8422-2 and Surlyn(copyright) 8422-3, it is noted that the high acid Surlyn(copyright) 8422-2 and 8422-3 ionomers have a higher tensile yield, lower elongation, slightly higher Shore D hardness and much higher flexural modulus. Surlyn(copyright) 8920 contains 15 weight percent methacrylic acid and is 59% neutralized with sodium.
In addition, Surlyn(copyright) SEP-503-1 (zinc cation) and Surlyn(copyright) SEP-503-2 (magnesium cation) are high acid zinc and magnesium versions of the Surlyn(copyright) AD 8422 high acid ionomers. When compared to the Surlyn(copyright) AD 8422 high acid ionomers, the Surlyn(copyright) SEP-503-1 and SEP-503-2 ionomers can be defined as follows:
Furthermore, Surlyn(copyright) 8162 is a zinc cation ionomer resin containing approximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acid copolymer that has been 30-70% neutralized. Surlyn(copyright) 8162 is currently commercially available from DuPont.
Further examples of the pre-neutralized high acid acrylic acid based ionomers suitable for use in the present invention include the Escor(copyright) or Iotek(trademark) high acid ethylene acrylic acid ionomers recently produced by Exxon. In this regard, Escor(copyright) or Iotek(trademark) 959 is a sodium ion neutralized ethylene-acrylic acid copolymer and Escor(copyright) or Iotek(trademark) 960 is a zinc neutralized ethylene-acrylic acid copolymer. According to Exxon, Iotek(trademark) 959 and Iotek(trademark) 960 contain from about 19.0 to about 21.0% by weight acrylic acid with approximately 30 to about 70 percent of the acid groups neutralized with sodium and zinc ions respectfully. The physical properties of these high acid acrylic acid based ionomers are as follows:
As briefly discussed above, the cover composition of the invention comprises of about 0-90 percent by weight of at least one neutralized acid copolymer, preferably about 0-50 percent, and most preferably 0-75 percent acid copolymer. At the same time, the cover may comprise about 100-10 percent by weight of at least one neutralized ethylene alkyl acrylate copolymer, preferably 100-25 percent, and most preferably 100-50 percent ethylene alkyl acrylate copolymer.
Generally, the ethylene alkyl acrylate copolymers used herein include the copolymers of ethylene and acrylic or methacrylic esters of linear, branched or cyclic alkanols. Preferably, the copolymers contain from about 1-30 weight percent alkyl acrylate and from about 99-70 weight percent ethylene.
Ethylene alkyl acrylate copolymers which may be used include, among others, ethylene-ethyl acrylate (EEA), ethylene-methyl acrylate (EMA), and ethylene-butyl acrylate (EBA) copolymers.
Ethylene-ethyl acrylate (EEA) copolymers are made by the polymerization of ethylene units with randomly distributed ethylene acrylate (EA) comonomer groups. The (EEA) copolymers contain up to about 30% by weight of ethylene acrylate. They are tough, flexible products having a relatively high molecular weight. They have good flexural fatigue and low temperature properties (down to xe2x88x9265xc2x0 C.). In addition, EEA resists environmental stress cracking as well as ultraviolet radiation.
Examples of ethylene-ethyl acrylate which may be utilized include Bakelite(copyright) DPD-6169 or Bakelite(copyright) DPD-6182 available from Union Carbide. Properties of these and other suitable ethylene-ethyl acrylate copolymers include:
EEA is similar to ethylene vinyl acetate (EVA) in its density-property relationships and high-temperature resistance. In addition, like EVA, EEA is not resistant to aliphatic and aromatic hydrocarbons. For comparison purposes, some typical properties of ionomers as well as ethylene vinyl acetate and ethylene ethyl acrylate are provided below:
Ethylene-methyl acrylate (EMA) copolymers contain up to about 30% by weight of methyl acrylate and yield blown films having rubberlike limpness and high impact strength. These copolymers may be useful in coating and laminating applications as a result of their good adhesion to commonly used substrates. EMAs have good heat-seal characteristics.
Ethylene-methyl acrylate copolymers are manufactured by reacting, at high temperatures and pressures, methyl-acrylate monomers with ethylene and free radical initiators. Polymerization occurs such that the methyl acrylate forms random pendant groups on the polyethylene backbone. The acrylic functionality decreases resin crystallinity and increases polarity to enhance resin properties. The properties depend on molecular weight (determined by melt index) and percent crystallinity. Percent crystallinity is determined by comonomer incorporation. As the comonomer content increases, the film become softer; tougher, and easier to heat seal.
EMA films have low modulus ( less than 10,000 psi), low melting points, and good impact strength. In addition, the EMA resins are highly polar, and as a result are compatible with olefinic and other polymers. They adhere well to many substrates including LDPE, LLDPE, and EVA.
Examples of ethylene-methyl acrylate which may be used in the golf ball cover compositions of the present invention include the Optema(trademark) or Escor(copyright) EMA copolymer resins available from Exxon Chemical Company. The Optema(trademark)/Escor(copyright) EMA resins are thermally stable ethylene methyl acrylate resins which will accept up to 65% or more fillers and pigments without losing their properties. They are more thermally stable than EVAs and can be extruded or molded over a range of 275-625xc2x0 F. (compared to an EVA limit of 450xc2x0 F.). EMAs are generally not corrosive when compared to EVAs, EAAs and ionomers. Some of the typical properties associated with the various grades of Optema(trademark) EMA resins are found in the following Table 13:
Certain developmental grades of Optema(trademark) EMAs may be used in formulating the golf ball covers herein. These developmental grades of resins are designated xe2x80x9cXSxe2x80x9d. Pertinent properties of XS-11.04, 12.04 and 13.04 are set forth above in Table 13. Melt index and methyl acrylate content of these and certain others are set forth in the following Table 14:
Ethylene butyl acrylates (EBA) can also be included in the invention. These are generally similar to ethylene methyl acrylate (EMA) with improved low temperature impact strength and high clarity.
Chevron Chemical Company""s ethylene-butyl acrylate copolymer, EBAC(trademark), is stable at high temperatures, and may be processed as high as 600xc2x0 F. Typical properties (or average values) of certain EBAC(trademark) copolymers are set forth below in Table 15.
The cation salts utilized in the invention for neutralizing the ethylene alkyl copolymers are those salts which provide the metal cations capable of hydrolyzing and neutralizing, to various extents, the carboxylic acid esters groups of the ethylene alkyl copolymers. This converts the alkyl ester into a metal salt of the acid. These metal cation salts include oxide, carbonate or hydroxide salts of alkali metals such as lithium, sodium and potassium or mixtures thereof.
Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium carbonate and lithium oxide. Examples of sodium ion sources are sodium hydroxide, sodium oxide and sodium carbonate. Sources for the potassium ion include potassium hydroxide, potassium oxide and potassium carbonate.
The amount of metal cation salt (preferably an alkali metal cation salt) reacted with the ethylene alkyl acrylate copolymer varies depending upon such factors as the reactivity of the salt and the copolymer used, reaction conditions (temperature, pressure, moisture content, etc.) and the desired level of conversion. Preferably, the conversion reaction occurs through saponification wherein the carboxylic acid esters of the ethylene alkyl acrylate copolymer are converted by alkaline hydrolysis to form the salt of the acid and alcohol. Examples of such saponification reactions are set forth in U.S. Pat. Nos. 3,970,626, 4,638,034 and 5,218,057 and are incorporated herein by reference.
The products of the conversion reaction are an alkanol (the alkyl group of which comes from the alkyl acrylate comonomer) and a terpolymer of ethylene, alkyl acrylate, and an alkali metal salt of the (meth) acrylic acid. The degree of conversion or saponification is variable depending on the amount of alkali metal cation salt used and the saponification conditions. Generally from about 10% to about 60% of the ester groups are converted during the saponification reaction. The alkanol and other by products can be removed by normal separation processes leaving the remaining metal cation neutralized (or hydrolysized) ester-based ionomer resin reaction product.
Alternatively, the ethylene alkyl acrylate copolymer included in the invention can be commercially obtained in a pre-neutralized or saponifized condition. For example, a number of metal cation neutralized ester-based ionomer resins produced under the saponification process of U.S. Pat. No. 5,218,057 are available from the Chevron Chemical Company of Houston, Tex. In this regard, Chevron sells several sodium neutralized ester-based ionomer resins chemically based on ethylene methyl acrylate and ethylene butyl acrylate under the trademark xe2x80x9cIMAC(trademark)xe2x80x9d. According to Chevron, the IMAC(trademark) sodium neutralized ester-based ionomer resins offer property differences over the Suryln(copyright) and Iotek(trademark)(trademark) resins. This is shown below.
Examples of such sodium neutralized ester-based ionomer resins are the development specialty (xe2x80x9cDSxe2x80x9d) resins available from Chevron under the designation IMAC DS 4032, DS 3076, DS 1993 and DS 3088. According to Chevron, these materials are based upon ethylene methyl acrylates (EMA) having 10-25% methyl acylate and the level of neutralization for the DS 4032, DS 3076 and DS 1993 is slightly less than 50% (Chevron DS 3088 has a lower level of neutralization). Along these lines, the following typical properties are provided by Chevron for IMAC DS 4032:
In addition, the Chevron IMAC ionomer resins have the following general characteristics:
Additional compatible additive materials may also be added to the cover compositions of the present invention, such as dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Painsfield, N.J.), and pigments, i.e. white pigments such as titanium dioxide (for example Unitane 0-110) zinc oxide, and zinc sulfate, as well as fluorescent pigments. As indicated in U.S. Pat. No. 4,884,814, the amount of pigment and/or dye used in conjunction with the polymeric cover composition depends on the particular base ionomer mixture utilized and the particular pigment and/or dye utilized. The concentration of the pigment in the polymeric cover composition can be from about 1% to about 10% as based on the weight of the base ionomer mixture. A more preferred range is from about 1% to about 5% as based on the weight of the base ionomer mixture. The most preferred range is from about 1% to about 3% as based on the weight of the base ionomer mixture. The most preferred pigment for use in accordance with this invention is titanium dioxide.
Moreover, since these are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added to the cover stock composition to impart a blue white appearance thereto. However, if different hues of the color white are desired, different pigments can be added to the cover composition at the amounts necessary to produce the color desired.
In addition, it is within the purview of this invention to add to the cover compositions of this invention compatible materials which do not affect the basic novel characteristics of the composition of this invention. Among such materials are antioxidants (i.e. Santonox R), antistatic agents, stabilizers and processing aids. The cover compositions of the present invention may also contain softening agents, such as plasticizers, etc., and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.
Furthermore, optical brighteners, such as those disclosed in U.S. Pat. No. 4,679,795, may also be included in the cover composition of the invention. Examples of suitable optical brighteners which can be used in accordance with this invention are Unitex OB as sold by the Ciba-Geigy Chemical Company, Ardaley, N.Y. Unitex OB is thought to be 2,5-Bis (5-tert-butyl-2-benzoxazoly) thiophene. Examples of other optical brighteners suitable for use in accordance with this invention are as follows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936. Leucopure EGM is thought to be 7-(2h-naphthol (1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-20G2 is sold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park, Union, N.J. 07083, and is thought to be a pyrazoline derivative, Eastobrite OB-1 as sold by Eastman Chemical Products, Inc. Kingsport, Tenn., is thought to be 4,4-Bis (-benzoxaczoly) stilbene. The above-mentioned Uvitex and Eastobrite OB-1 are preferred optical brighteners for use in accordance with this invention.
Moreover, since many optical brighteners are colored, the percentage of optical brighteners utilized must not be excessive in order to prevent the optical brightener from functioning as a pigment or dye in its own right.
The percentage of optical brighteners which can be used in accordance with this invention is from about 0.01% to about 0.5% as based on the weight of the polymer used as a cover stock. A more preferred range is from about 0.05% to about 0.25% with the most preferred range from about 0.10% to about .020% depending on the optical properties of the particular optical brightener used and the polymeric environment in which it is a part.
Generally, the additives are admixed with a ionomer to be used in the cover composition to provide a masterbatch (M.B.) of desired concentration and an amount of the masterbatch sufficient to provide the desired amounts of additive is then admixed with the copolymer blends.
The cover compositions of the present invention may be produced according to conventional melt blending procedures. In this regard, the ionomeric resins are blended along with the masterbatch containing the desired additives in a Banbury type mixer, two-roll mill, or extruded prior to molding. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state until molding is desired. Alternatively a simple dry blend of the pelletized or granulated resins and color masterbatch may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. If necessary, further additives such as an inorganic filler, etc., may be added and uniformly mixed before initiation of the molding process.
Moreover, golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by injection molding or compression molding the novel cover compositions about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 inches or greater and weighing about 1.620 ounces. The standards for both the diameter and weight of the balls are established by the United States Golf Association (U.S.G.A.). Although both solid core and wound cores can be utilized in the present invention, as a result of their lower cost and superior performance, solid molded cores are preferred over wound cores.
Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis: content polybutadiene and a metal salt of an xcex1, xcex2, ethylenically unsaturated carboxylic acid such as zinc mono or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. In addition, larger amounts of metal oxide than those that are needed to achieve the desired coefficient may be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing or cross-linking reaction takes place.
The term xe2x80x9csolid coresxe2x80x9d as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multilayer and/or non-wound cores (such as those described in U.S. Pat. No. 4,848,770).
Wound cores are generally produced by winding a very large elastic thread around a solid or liquid filled balloon center. The elastic thread is wound around the center to produce a finished core of about 1.4 to 1.6 inches in diameter, generally. Since the-core material is not an integral part of the present invention, a detailed discussion concerning the specific types of core materials which may be utilized with the cover compositions of the invention are not specifically set forth herein. In this regard, the cover compositions of the invention may be used in conjunction with any standard golf ball core.
As indicated, the golf balls of the present invention may be produced by forming covers consisting of the compositions of the invention around cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380xc2x0 F. to about 450xc2x0 F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200-300xc2x0 F. for 2-10 minutes, followed by cooling at 50-70xc2x0 F. for 2-10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50xc2x0 F. to about 100xc2x0 F. After molding the golf balls produced may undergo various further finishing steps such as buffing, painting, and marking as disclosed in U.S. Pat. No. 4,911,451.
The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight (pbw). It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.